This invention relates to an aqueous pigment dispersion used for aqueous coating compositions.
It is well known that since aqueous paints scarcely require organic solvents, there are no fears of environmental pollution and fire so that such aqueous paints may safely be adopted for household use, and for this reason, the importance of the aqueous paints has recently increased.
However, in spite of the advantages of the aqueous paints as mentioned above, the aqueous paints have not yet replaced organic solvent paints. Of course, this is because the aqueous paints have fatal disadvantages such as poor chemical resistance and poor water resistance. Concerning the causes for these disadvantages, it may be considered that the surface active agent employed for an emulsion polymerization decreases the chemical and water resistance in respect of an emulsion type coating composition, and on the other hand, it may be considered that there is a difficulty for making hydrophilic groups on the water-soluble resin sufficiently hydrophobic in respect of a water soluble coating composition. Under the circumstances, in emulsion type coating compositions, a process of emulsion polymerization in which no surface active agent is employed has been developed so that some effects as to the improvement of water resistance could have been obtained. However, even in this case, use of a usual surface active agent at the step of adding a pigment cannot be avoided, so that the expected improvement as to the properties of the aqueous paints is cancelled.